As is known, some types of microreactors, such as microreactors for biochemical analyses, comprise arrays of wells for receiving small volumes of reagents in the form of liquids or gels, especially water-based ones, and/or given volumes of specimens to be analyzed. Microreactors of this type respond, amongst other things, to the widespread need of increasing the level of parallelism in the execution of analysis procedures, for example for diagnostic or experimental purposes. Each well may be prepared with different reagents, and hence various analytical procedures may be conducted simultaneously on a single biological sample.
In a typical application, the wells are prepared for performing reactions of amplification of nucleic acids, for example by PCR (Polymerase Chain Reaction). In addition to the mixture of reagents necessary for amplification, loaded in each well are respective detector sequences, which comprise single stranded oligonucleotides capable of binding to corresponding DNA or RNA sequences that may be present in the biological sample. This way, each well may be dedicated to recognition of a specific target sequence (for example, corresponding to a specific pathogenic agent).
Handling of small volumes of biological sample may, however, create difficulties, particularly in loading of the wells. All the wells must receive a sufficient amount of biological sample. Once loading has been carried out, moreover, the contents of each well must be kept segregated from those of the other wells during the reactions in order to prevent any contamination that might jeopardize the outcome of the processes.
The biological sample may be introduced into the wells manually, using pipettes. In this case, the microreactors are initially uncovered to enable access to the wells, and are closed only subsequently. Manual loading presents evident limits both owing to the impossibility of treating very small volumes (a few microliters) and because contaminations are relatively likely to occur.
In other microreactors, the specimen is loaded in a common reservoir and distributed to the wells via microchannels, in which the fluid advances by capillary action. In this case, very small volumes of fluid can be treated. But, problems may arise owing to the formation of bubbles in the microchannels, thus impeding flow and reducing the amount of available liquid.
When capillary forces are involved, air bubbles may easily remain trapped during loading. The geometry and the affinity of the specimen with the material forming the microchannels may produce highly unstable menisci. The edges of the menisci may join up in given conditions, and the air bubbles may be trapped inside the liquid. A single air bubble may occupy a relatively wide portion of the microchannels and prevent an adequate volume of specimen from reaching one or more wells. Analysis may be impaired because important process parameters, such as volume, equilibrium of the reagents, pressure and temperature, are affected by the presence of bubbles.
The aim of the present disclosure is to provide a microreactor and a method for loading a liquid into a microreactor that will enable the limitations described to be overcome.